Traveling wave nuclear fission reactor, fuel assembly, and method of controlling burnup therein

ABSTRACT

A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims the benefit of theearliest available effective filing date from the following listedapplications (the “Related Applications”) (e.g., claims earliestavailable priority dates for other than provisional patent applicationsor claims benefits under 35 USC §119(e) for provisional patentapplications, for any and all parent, grandparent, great-grandparent,etc. applications of the Related Applications).

RELATED APPLICATIONS

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 11/605,943, entitled AUTOMATED NUCLEAR POWERREACTOR FOR LONG-TERM OPERATION, naming RODERICK A. HYDE, MURIEL Y.ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors,filed 28 Nov. 2006, which is currently co-pending, or is an applicationof which a currently co-pending application is entitled to the benefitof the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 11/605,848, entitled METHOD AND SYSTEM FORPROVIDING FUEL IN A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y.ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors,filed 28 Nov. 2006, which is currently co-pending, or is an applicationof which a currently co-pending application is entitled to the benefitof the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 11/605,933, entitled CONTROLLABLE LONG TERMOPERATION OF A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y.ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors,filed 28 Nov. 2006, which is currently co-pending, or is an applicationof which a currently co-pending application is entitled to the benefitof the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 12/069,907, entitled MODULAR NUCLEAR FISSIONREACTOR, naming CHARLES E. AHLFELD, JOHN ROGERS GILLELAND, RODERICK A.HYDE, MURIEL Y. ISHIKAWA, DAVID G. MCALEES, NATHAN P. MYHRVOLD, CHARLESWHITMER, AND LOWELL L. WOOD, JR. as inventors, filed 12 Feb. 2008, whichis currently co-pending, or is an application of which a currentlyco-pending application is entitled to the benefit of the filing date.

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 12/069,908, entitled NUCLEAR FISSION IGNITER,naming CHARLES E. AHLFELD, JOHN ROGERS, GILLELAND, RODERICK A. HYDE,MURIEL Y. ISHIKAWA, DAVID G. MCALEES, NATHAN P. MYHRVOLD, CHARLESWHITMER, AND LOWELL L. WOOD, JR. as inventors, filed 12 Feb. 2008, whichis currently co-pending, or is an application of which a currentlyco-pending application is entitled to the benefit of the filing date.

The United States Patent Office (USPTO) has published a notice to theeffect that the USPTO's computer programs require that patent applicantsreference both a serial number and indicate whether an application is acontinuation or continuation-in-part. Stephen G. Kunin, Benefit ofPrior-Filed Application, USPTO Official Gazette Mar. 18, 2003, availableat http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm.The present Applicant Entity (hereinafter “Applicant”) has providedabove a specific reference to the application(s) from which priority isbeing claimed as recited by statute. Applicant understands that thestatute is unambiguous in its specific reference language and does notrequire either a serial number or any characterization, such as“continuation” or “continuation-in-part,” for claiming priority to U.S.patent applications. Notwithstanding the foregoing, Applicantunderstands that the USPTO's computer programs have certain data entryrequirements, and hence Applicant is designating the present applicationas a continuation-in-part of its parent application as set forth above,but expressly points out that such designations are not to be construedin any way as any type of commentary and/or admission as to whether ornot the present application contains any new matter in addition to thematter of its parent application.

All subject matter of the Related Application and of any and all parent,grandparent, great-grandparent, etc. applications of the RelatedApplications is incorporated herein by reference to the extent suchsubject matter is not inconsistent herewith.

BACKGROUND

This application generally relates to control of nuclear reactions andmore particularly relates to a traveling wave nuclear fission reactor,fuel assembly, and a method of controlling burnup therein.

It is known, in an operating nuclear fission reactor, that neutrons of aknown energy are absorbed by nuclides having a high atomic mass. Theresulting compound nucleus separates into fission products that includetwo lower atomic mass fission fragments and also decay products.Nuclides known to undergo such fission by neutrons of all energiesinclude uranium-233, uranium-235 and plutonium-239, which are fissilenuclides. For example, thermal neutrons having a kinetic energy of0.0253 eV (electron volts) can be used to fission U-235 nuclei.Thorium-232 and uranium-238, which are fertile nuclides, will notundergo induced fission, except with fast neutrons that have a kineticenergy of at least 1 MeV (million electron volts). The total kineticenergy released from each fission event is about 200 MeV. This kineticenergy is eventually transformed into heat.

Moreover, the fission process, which starts with an initial source ofneutrons, liberates additional neutrons as well as transforms kineticenergy into heat. This results in a self-sustaining fission chainreaction that is accompanied by continued energy release.

A traveling wave Pyrotron for continuous operation is disclosed in U.S.Pat. No. 3,093,569, issued Jun. 11, 1963 in the names of Richard F.Post, et al. and titled “Traveling Wave Pyrotron.” This patent disclosesa continuous operating reactor or device for increasing the energy anddensity of plasma and conducting nuclear reactions therein. An object ofthe invention is to provide a Pyrotron where traveling magnetic wavesare employed to accomplish trapping, heating and energy recovery ofcharged particles within individual containment zones, each of whichprogresses along the machine with time. However, this patent does notappear to disclose a traveling wave nuclear fission reactor, fuelassembly, and a method of controlling burnup therein, as described andclaimed herein.

U.S. Pat. No. 3,799,839 issued Mar. 6, 1974 in the names of David L.Fischer, et al. and titled “Reactivity And Power Distribution Control OfNuclear Reactor” discloses a spatial distribution, amount, density andconfiguration of burnable poison to control a predetermined amount ofexcess reactivity and to maintain a constant or stationary powerdistribution during the operating cycle of a nuclear reactor core.According to this patent, it is an object of the invention to provide anarrangement of burnable poison in a nuclear reactor core which willprovide a substantially stationary power distribution in the corethroughout the period of the operating cycle. Also, according to thispatent, other objects are achieved in accordance with the invention bydetermining consistent power and concomitant reactivity distributionsfor the operating cycles: by determining the resulting excess localreactivity, and by providing burnable poison in amount, density andconfiguration, spatially distributed to substantially match the changesin excess local reactivity throughout the period of the operating cycle.However, this patent does not appear to disclose a traveling wavenuclear fission reactor, fuel assembly, and a method of controllingburnup therein, as described and claimed herein.

U.S. Pat. No. 3,489,646 issued Jan. 13, 1970 in the names of Jean PaulVan Dievoet, et al. and titled “Method of Pulsating or Modulating aNuclear Reactor” relates to a method of pulsating or modulating theoperation of a nuclear reactor. This patent discloses modulating thereactor by periodically varying the neutron flux density. According tothis patent, operation of a nuclear reactor is controlled by moving oneor more structures containing at least at certain localities, an amountof neutron-active substance, at a place outside the nuclear fissionregion of the reactor, and thereby modify, in dependence upon the speedof the structure, a neutron flow issuing from the reactor core. Thespecimens of neutron-active material which thus modify the reactivity ofthe reactor system from the outside may be neutron-generating and/orneutron-influencing material, such as fissionable material, reflectormaterial or other neutron-influencing substance. However, this patentdoes not appear to disclose a traveling wave nuclear fission reactor,fuel assembly, and a method of controlling burnup therein, as describedand claimed herein.

None of the art recited hereinabove appears to disclose a traveling wavenuclear fission reactor, fuel assembly, and a method of controllingburnup therein, as described and claimed herein.

Therefore, what are needed are a traveling wave nuclear fission reactor,fuel assembly, and a method of controlling burnup therein, as describedand claimed herein.

SUMMARY

According to an aspect of this disclosure, there is provided a method ofcontrolling burnup in a traveling wave nuclear fission reactor capableof emitting a neutron flux, comprising modulating the neutron fluxemitted by the traveling wave nuclear fission reactor.

According to another aspect of this disclosure, there is provided amethod of controlling burnup in a traveling wave nuclear fission reactorcapable of emitting a neutron flux, comprising modulating the neutronflux emitted by the traveling wave nuclear fission reactor, the neutronflux defining a burnfront.

According to a further aspect of this disclosure, there is provided atraveling wave nuclear fission reactor, comprising a nuclear reactorcore; and a nuclear fission reactor fuel assembly disposed in thereactor core, the nuclear fission reactor fuel assembly being configuredto achieve a burnup value that or below a predetermined burnup value.

According to an additional aspect of this disclosure, there is provideda traveling wave nuclear fission reactor, comprising a nuclear reactorcore capable of producing a burnfront therein; a nuclear fission reactorfuel assembly disposed in the nuclear reactor core; a neutroninteractive material disposed in the nuclear fission reactor fuelassembly; and a control system configured to control disposition of thenuclear interactive material in response to a parameter associated withthe burnfront.

According to yet another aspect of this disclosure, there is provided atraveling wave nuclear fission reactor capable of controlling burnuptherein, comprising a reactor pressure vessel; a nuclear fission reactorfuel assembly sealingly disposed in the pressure vessel, the nuclearfission reactor fuel assembly including a neutron interactive materialarranged in a predetermined loading pattern; and a removable nuclearfission igniter capable of being disposed in neutronic communicationwith the neutron interactive material, the nuclear fission ignitercapable of igniting a deflagration wave burnfront traveling through theneutron interactive material.

A feature of the present disclosure is the provision of neutron absorbermaterial in the form of a control rod, reflector, or neutron emittingmaterial or other absorber material that enhances absorption at alocation relative to a deflagration wave burnfront.

In addition to the foregoing, various other method and/or device aspectsare set forth and described in the teachings such as text (e.g., claimsand/or detailed description) and/or drawings of the present disclosure.

The foregoing is a summary and thus may contain simplifications,generalizations, inclusions, and/or omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Inaddition to the illustrative aspects, embodiments, and featuresdescribed above, further aspects, embodiments, and features will becomeapparent by reference to the drawings and the following detaileddescription.

BRIEF DESCRIPTION OF THE FIGURES

While the specification concludes with claims particularly pointing-outand distinctly claiming the subject matter of the present disclosure, itis believed the disclosure will be better understood from the followingdetailed description when taken in conjunction with the accompanyingdrawings. In addition, the use of the same symbols in different drawingswill typically indicate similar or identical items.

FIG. 1 is a view in partial elevation of a nuclear fission reactorarrangement;

FIG. 2 is a graph showing cross-section versus neutron energy;

FIG. 3 is a graph showing cross-section versus neutron energy togetherwith ratios of those cross-sections versus neutron energy;

FIG. 4 is a view in partial elevation of a generic representation of anuclear fission reactor fuel assembly;

FIG. 5 is a view in partial vertical section of a nuclear fuel rod;

FIG. 6 is a view in partial vertical section of a control rod;

FIG. 7 is a view in partial vertical section of a reflector rod;

FIG. 8 is a view in horizontal section of a first embodiment fuelassembly, this view showing two oppositely-disposed and symmetricaldeflagration burn fronts initiated by an igniter and also showing afirst fuel loading pattern;

FIG. 9 is a view in horizontal section of one-half of the firstembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts;

FIG. 10 is a graph showing a first control function comprising percentof control rod insertion versus distance from the igniter, this firstcontrol function corresponding to the first fuel loading pattern of thefirst embodiment fuel assembly;

FIG. 11 is a view in horizontal section of one-half of a secondembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a second fuel loading pattern;

FIG. 12 is a graph showing a second control function comprising percentof control insertion versus distance from the igniter, this secondcontrol function corresponding to the second fuel loading pattern of thesecond embodiment fuel assembly;

FIG. 13 is a view in horizontal section of one-half of a thirdembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a third fuel loading pattern;

FIG. 14 is a graph showing a third control function comprising percentof control rod insertion versus distance from the igniter, this thirdcontrol function corresponding to the third fuel loading pattern of thethird embodiment fuel assembly;

FIG. 15 is a view in horizontal section of one-half of a fourthembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a fourth fuel loading pattern;

FIG. 16 is a graph showing a fourth control function comprising percentof control rod insertion versus distance from the igniter, this fourthcontrol function corresponding to the fourth fuel loading pattern of thefourth embodiment fuel assembly;

FIG. 17 is a view in horizontal section of one-half of a fifthembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a fifth fuel loading pattern;

FIG. 18 is a graph showing a fifth control function comprising percentof control rod insertion versus distance from the igniter, this fifthcontrol function corresponding to the fifth fuel loading pattern of thefifth embodiment fuel assembly;

FIG. 19 is a view in horizontal section of one-half of a sixthembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a sixth fuel loading pattern;

FIG. 20 is a graph showing a sixth control function comprising percentof control rod insertion versus distance from the igniter, this sixthcontrol function corresponding to the sixth fuel loading pattern of thesixth embodiment fuel assembly;

FIG. 21 is a view in horizontal section of one-half of a seventhembodiment fuel assembly, this view showing one of theoppositely-disposed and symmetrical deflagration burn fronts and alsoshowing a seventh fuel loading pattern;

FIG. 22 is a graph showing a seventh control function comprising percentof control rod insertion versus distance from the igniter, this seventhcontrol function corresponding to the seventh fuel loading pattern ofthe seventh embodiment fuel assembly;

FIG. 23 is a graph illustrating a linear relationship betweendeflagration burnfront velocity and inverse burnup percent versus degreeof wave control function;

FIG. 23A is a graph showing an exemplary spatial distribution of neutronflux comprising neutron flux versus distance from the igniter, thespatial distribution being representative of the burnfront according toan exemplary control function;

FIG. 23B is a graph showing a control function corresponding to thespatial distribution shown in FIG. 23A, this graph comprising percent ofcontrol rod insertion versus distance from the igniter;

FIG. 23C is a graph showing an exemplary spatial distribution of neutronflux comprising neutron flux versus distance from the igniter, thespatial distribution being representative of the burnfront according toan exemplary control function;

FIG. 23D is a graph showing a control function corresponding to thespatial distribution shown in FIG. 23C, this graph comprising percent ofcontrol rod insertion versus distance from the igniter;

FIG. 23E is a graph showing an exemplary spatial distribution of neutronflux comprising neutron flux versus distance from the igniter, thespatial distribution being representative of the burnfront;

FIG. 23F is a graph showing a control function corresponding to thespatial distribution shown in FIG. 23E, this graph comprising percent ofcontrol rod insertion versus distance from the igniter; and

FIGS. 24-65 are flowcharts of illustrative methods of controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein.

In addition, the present application uses formal outline headings forclarity of presentation. However, it is to be understood that theoutline headings are for presentation purposes, and that different typesof subject matter may be discussed throughout the application (e.g.,device(s)/structure(s) may be described under process(es)/operationsheading(s) and/or process(es)/operations may be discussed understructure(s)/process(es) headings; and/or descriptions of single topicsmay span two or more topic headings). Hence, the use of the formaloutline headings is not intended to be in any way limiting.

Moreover, the herein described subject matter sometimes illustratesdifferent components contained within, or connected with, differentother components. It is to be understood that such depictedarchitectures are merely exemplary, and that in fact many otherarchitectures may be implemented which achieve the same functionality.In a conceptual sense, any arrangement of components to achieve the samefunctionality is effectively “associated” such that the desiredfunctionality is achieved. Hence, any two components herein combined toachieve a particular functionality can be seen as “associated with” eachother such that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled,” to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable,” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents, and/or wirelessly interactable, and/or wirelesslyinteracting components, and/or logically interacting, and/or logicallyinteractable components.

In some instances, one or more components may be referred to herein as“configured to,” “configurable to,” “operable/operative to,”“adapted/adaptable,” “able to,” “conformable/conformed to,” etc. Thoseskilled in the art will recognize that “configured to” can generallyencompass active-state components and/or inactive-state componentsand/or standby-state components, unless context requires otherwise.

Some considerations regarding various embodiments disclosed herein aregiven by way of overview but are not to be interpreted as limitations.Also, some of the embodiments disclosed herein reflect attainment of allof the considerations discussed below. On the other hand, some otherembodiments disclosed herein reflect attainment of selectedconsiderations, and need not accommodate all of the considerationsdiscussed hereinbelow. Portions of the following discussion includeinformation excerpted from a paper titled “Completely Automated NuclearPower Reactors for Long-Term Operation: III. Enabling Technology ForLarge-Scale, Low-Risk, Affordable Nuclear Electricity” by Edward Teller,Muriel Ishikawa, Lowell Wood, Roderick Hyde, and John Nuckolls,presented at the July 2003 Workshop of the Aspen Global ChangeInstitute, University of California Lawrence Livermore NationalLaboratory publication UCRL-JRNL-122708 (2003). (This paper was preparedfor submittal to Energy, The International Journal, 30 Nov. 2003, theentire contents of which are hereby incorporated by reference).

As previously mentioned, for every neutron that is absorbed in a fissilenuclide which leads to a fission event, more than one neutron isliberated until the fissile nuclei are depleted. This phenomenon is usedin a commercial nuclear reactor to produce continuous heat that, inturn, is beneficially used to generate electricity.

However, a consideration in reactor design and operation is heat damageto reactor structural materials due to “peak” temperature (i.e., hotchannel peaking factor) which occurs due to a combination of unevenneutron flux, coolant flow, fuel composition and power distribution inthe reactor. Heat damage results if the peak temperature exceedsmaterial limits. This can happen regardless of the extent of burn-up(i.e., cumulative amount of energy generated per unit mass of fuel),which is usually expressed in units of megawatt-days per metric tonne ofheavy metal fuel (MWd/MTHM) or gigawatt-days per metric tonne of heavymetal fuel (GWd/MTHM). A “reactivity change” (i.e., change in theresponsiveness of the reactor) may be produced because of fuel burnup.More specifically, “reactivity change” is related to the relativeability of the reactor to produce more or less neutrons than the exactamount to sustain the critical chain reaction. Responsiveness of areactor is typically characterized as the time derivative of areactivity change causing the reactor to increase or decrease in powerexponentially where the time constant is known as the reactor period. Inthis regard, control rods made of neutron absorbing material aretypically used to adjust and control the changing reactivity and reactorresponsiveness. Such control rods are reciprocated in and out of thereactor core to variably control neutron absorption and thus the neutronflux level and reactivity in the core. The neutron flux level isdepressed in the vicinity of the control rod and potentially higher inareas remote from the control rod. Thus, the neutron flux is not uniformacross the reactor core. This results in higher fuel burnup in thoseareas of higher flux. Also, it may be appreciated by a person ofordinary skill in the art of nuclear power production that flux andpower density variations are due to many factors. Proximity to a controlrod may or may not be the primary factor. For example, the fluxtypically drops significantly at core boundaries with no nearby controlrod. These effects, in turn, may cause overheating or high temperaturesin those areas of higher flux. Such peak temperatures may undesirablyreduce the operational life of structures subjected to such peaktemperatures by altering the mechanical properties of the structures.Also, reactor power density, which is proportional to the product of theneutron flux and the fissile fuel concentration, is limited by theability of core structural materials to withstand such high temperatureswithout damage. Therefore, it is desirable to avoid structural damagedue to high temperatures caused by high fuel burnup.

Another consideration in reactor design and operation is irradiationdamage to structural materials contained in the nuclear reactor core dueto high fuel burnup. Such irradiation damage may be expressed in termsof displacements per atom (DPA), which includes information on theresponse of the material (i.e., displaced atoms), as well as the fastneutron fluence to which the material was exposed. DPA is proportionalto burnup and is a calculated, representative measure of radiationdamage which accounts for not only the dose and type of irradiation, butalso includes a measure of the material's response to the irradiation.In this regard, some structural materials used in reactor corestructures may become embrittled when exposed to neutrons releasedduring the fission process. It is desirable to maintain such irradiationdamage to reactor structural materials within known limits in order toensure structural integrity and safe operation of the reactor.

Therefore, referring to FIG. 1, by way of example only and not by way oflimitation, there is shown a nuclear fission reactor arrangement,generally referred to as 10, to address the problems recitedhereinabove. Nuclear fission reactor arrangement 10 generateselectricity that is to be transmitted over a plurality of transmissionlines (not shown). Reactor arrangement 10 alternatively may be used toconduct tests to determine effects of neutron flux on reactor materials.

Referring again to FIG. 1, reactor arrangement 10 comprises a nuclearfission reactor, generally referred to as 20, that includes a pluralityof generic nuclear fission reactor fuel assemblies, generally referredto as 30 (only one of which is shown), disposed within a reactorpressure vessel 40, which in turn may be housed within a containmentstructure (not shown). By way of illustration only and not by way oflimitation, exemplary embodiments of generic fuel assembly 30 aredisclosed hereinbelow. Generic fuel assembly 30 may be surrounded by aneutron multiplier or reflector material (not shown) and a radiationshield (also not shown). In this case, the reflector material reducesneutron leakage from fuel assembly 30. An additional function of thereflector material is to substantially reduce the fast neutron fluenceseen by the outer portions of fuel assembly 30, such as its radiationshield, structural supports and containment structure. It alsoinfluences the performance of generic fuel assembly 30, so as to improvethe breeding efficiency and the specific power in the outermost portionsof generic fuel assembly 30. The radiation shield, on the other hand,further protects the biosphere from unintended release of radiation fromgeneric fuel assembly 30.

Referring yet again to FIG. 1, a primary coolant loop 50 carries heatfrom generic fuel assembly 30 to a steam generating heat exchangers 60.Primary loop 50 may be made from any suitable material, such asstainless steel. Thus, if desired, primary loop 50 may be made fromferrous alloys, non-ferrous alloys, zirconium-based alloys or otherstructural materials or composites. The coolant carried by primary loop50 may be a noble gas or mixtures thereof. Alternatively, the coolantmay be other fluids such as water (H₂O), or gaseous or supercriticalcarbon dioxide (CO₂). As another example, the coolant may be a liquidmetal such as sodium (Na) or lead (Pb) or alloys, such as lead-bismuth(Pb—Bi). Further, the coolant may be an organic-based coolant, such as apolyphenyl or a fluorocarbon. As the coolant carried by primary loop 50passes through steam generating heat exchanger 60, the coolant willgive-up its heat to a working fluid (not shown) residing in heatexchanger 60. The working fluid will vaporize to steam, when the workingfluid is water. In this case, the steam travels into a secondary loop 70that is isolated from primary loop 50 and that is coupled to aturbine-generator set 80 a and 80 b. Hence, heat exchanger 60 transfersheat to the working fluid in heat exchanger 60 and secondary loop 70 togenerate steam that is provided as the working fluid for rotatingturbine-generator set 80 a and 80 b. Turbine-generator set 80 a and 80 bgenerates electricity as it rotates, in a manner well understood in theart of electricity production from steam. A condenser 90 may be suitablycoupled to turbine-generator set 80 a and 80 b for condensing exhauststeam from turbine-generator set 80 a and 80 b from a vapor state to aliquid state.

Referring again to FIG. 1, a pump 100 is coupled to secondary loop 70and is in fluid communication with the working fluid carried bysecondary loop 70 for pumping the liquefied working fluid from condenser90 heat exchanger 60. Moreover, a pump 110 is coupled to primary loop 50and is in fluid communication with the reactor coolant carried byprimary loop 50 for pumping the reactor coolant through primary loop 50.Primary loop 50 carries the reactor coolant from generic fuel assembly30 to heat exchanger 60. Also, primary loop 50 carries the coolant fromheat exchanger 60 to pressure vessel 40. Pump 110 circulates the reactorcoolant through primary loop 50, including generic fuel assembly 30 andheat exchanger 60 in order to remove heat generated by fuel assembly 30during reactor operation or to remove residual decay heat when reactor20 is not operating. Removing heat from generic fuel assembly 30 reducesthe risk that generic fuel assembly 30 will overheat, which is highlyundesirable.

Referring now to FIGS. 2 and 3, generic fuel assembly 30 suitablyutilizes a fast neutron spectrum because the high absorptioncross-section of fission products for epithermal to thermal neutronsdoes not permit utilization of more than a small amount of thorium or ofthe more abundant uranium isotope, U²³⁸, in uranium-fueled embodiments,because of neutron absorption by fission products.

As best seen in FIG. 2, cross-sections for the dominant neutron-drivennuclear reactions of interest for the Th²³²-fueled embodiments areplotted over the neutron energy range 10⁻³-10⁷ eV. It can be seen thatlosses to radiative capture on fission product nuclei dominate neutroneconomies at near-thermal (approximately 0.1 eV) energies, but arecomparatively negligible above the resonance capture region (betweenapproximately 3 and 300 eV). Thus, operating with a fast neutronspectrum when attempting to realize a high-gain fertile-to-fissilebreeder can help to preclude neutron losses to fission products thatbuild-up within the core during operation. The radiative capturecross-sections for fission products shown are those for intermediate-Znuclei resulting from fast neutron-induced fission that have undergonesubsequent beta-decay to a negligible extent. Those in the centralportions of the burn-waves of embodiments of generic fuel assembly 30will have undergone some decay and thus will have somewhat higherneutron avidity. However, parameter studies have indicated that corefuel-burning results may be insensitive to the precise degree of suchdecay.

In FIG. 3, cross-sections for the dominant neutron-driven nuclearreactions of primary interest for the Th²³²-fueled embodiments areplotted over the most interesting portion of the neutron energy range,between >10⁴ and <10^(6.5) eV, in the upper portion of FIG. 3. Theneutron spectrum of embodiments of generic fuel assembly 30 peaks in the≧10⁵ eV neutron energy region. The lower portion of FIG. 3 contains theratio of these cross-sections versus neutron energy to the cross-sectionfor neutron radiative capture on Th²³², the fertile-to-fissile breedingstep (as the resulting Th²³³ swiftly beta-decays to Pa²³³, which thenrelatively slowly beta-decays to U²³³, analogously to theU²³⁹—Np²³⁹—Pu²³⁹beta decay-chain upon neutron capture by U²³⁸). Thus, itcan be seen that losses to radiative capture on fission products arecomparatively minimized for a reactor having a fast spectrum.

Turning now to FIGS. 4 and 5, generic fuel assembly 30 comprises fissileand/or fertile material, which may take the form of a plurality ofelongate nuclear fission reactor fuel rods 150 (only some of which areshown) arranged in a predetermined fuel loading pattern. Exemplaryembodiments of generic fuel assembly 30 are disclosed hereinbelow. Fuelrods 150 are sealingly contained within a leak-tight enclosure 155. Eachfuel rod 150 has nuclear fuel 160 disposed therein, which nuclear fuel160 is sealingly surrounded by a fuel rod cladding material 170. Anaverage burnup value for fuel assembly 30 is limited by claddingmaterial 170, which is the most pertinent structural material withinfuel assembly 30. Nuclear fuel 160 comprises the afore-mentioned fissilenuclide, such as uranium-235, uranium-233 or plutonium-239.Alternatively, nuclear fuel 160 may comprise a fertile nuclide, such asthorium-232 and/or uranium-238 which will be transmuted during thefission process into the fissile nuclides mentioned immediatelyhereinabove. A further alternative is that nuclear fuel 160 may comprisea predetermined mixture of fissile and fertile nuclides. By way ofexample only, and not by way of limitation, nuclear fuel 160 may be madefrom an oxide selected from the group consisting essentially of uraniummonoxide (UO), uranium dioxide (UO₂), thorium dioxide (ThO₂) (alsoreferred to as thorium oxide), uranium trioxide (UO₃), uraniumoxide-plutonium oxide (UO—PuO), triuranium octoxide (U₃O₈) and mixturesthereof. Alternatively, nuclear fuel 160 may substantially compriseuranium alloyed with other metals, such as, but not limited to,zirconium or thorium metal alloyed or unalloyed. As yet anotheralternative, nuclear fuel 160 may substantially comprise a carbide ofuranium (UC_(x)) or a carbide of thorium (ThC_(x)). For example, nuclearfuel 160 may be made from a carbide selected from the group consistingessentially of uranium monocarbide (UC), uranium dicarbide (UC₂),uranium sesquicarbide (U₂C₃), thorium dicarbide (ThC₂), thorium carbide(ThC) and mixtures thereof. As another non-limiting example, nuclearfuel 160 may be made from a nitride selected from the group consistingessentially of uranium nitride (U₃N₂), uranium nitride-zirconium nitride(U₃N₂Zr₃N₄), uranium-plutonium nitride ((U—Pu)N), thorium nitride (ThN),uranium-zirconium alloy (UZr) and mixtures thereof. Fuel rod claddingmaterial 170, which sealingly surrounds nuclear fuel 160, may be asuitable zirconium alloy, such as ZIRCOLOY™ (trademark of theWestinghouse Electric Corporation), which has known resistance tocorrosion and cracking. Cladding material 170 may be other materials, aswell, such as ferritic martensitic steels.

Referring to FIGS. 4 and 6, generic fuel assembly 30 further comprisesneutron absorber material, which may take the form of a plurality ofelongate neutron absorber or control rods 180 (only some of which areshown) with an associated control rod cladding 190. Control rods 180 arecapable of introducing negative reactivity into generic fuel assembly30. Control rods 180 may be in the form of “part-length” control rods192 (only some of which are shown) and/or “full-length” control rods 194(only some of which are shown). Full-length control rods 194 aresuitably positioned parallel to fuel rods 150 and extend the entirelength of fuel rods 150 when fully inserted into an enclosure 155.Part-length control rods 192 are also suitably positioned parallel tofuel rods 150, but do not extend the entire length of fuel rods 150 whenfully inserted into enclosure 155. There may be any number of suchpart-length and full-length control rods depending on the neutron fluxshaping design requirements for fuel assembly 30. A purpose offull-length control rods 192 is to reduce the rate of or stop thefission process occurring within generic fuel assembly 30 such as beforedecommissioning of reactor arrangement 10. Moreover, control rod and/orfuel rod configurations may deviate from the classic rod assembly typeconfigurations mentioned immediately hereinabove. For example, platetype fuel may be used. Additionally, the fuel rods may be perpendicular(or at any other angle) to the direction of burn.

Still referring to FIGS. 4 and 6, each control rod 180 comprises asuitable neutron absorber material 200 having an acceptably high neutroncapture cross-section. In this regard, absorber material 200 may be ametal or metalloid selected from the group consisting essentially oflithium, silver, indium, cadmium, boron, cobalt, hafnium, dysprosium,gadolinium, samarium, erbium, europium and mixtures thereof.Alternatively, absorber material 200 may be a compound or alloy selectedfrom the group consisting essentially of silver-indium-cadmium alloy,boron carbide, zirconium diboride, titanium diboride, hafnium diboride,gadolinium titanate, dysprosium titanate and mixtures thereof.Additionally, fuel rods that have been burned and have a high fissionproduct concentration may be used as part of the control. By way ofexample only, and not by way of limitation, each of such controls rods180 is, for example, vertically slidably movable inside respective onesof a plurality of control rod guide tubes (not shown) that werepreviously fixed within generic fuel assembly 30, such as duringfabrication of generic fuel assembly 30. A purpose of part-lengthcontrol rods 194 is to fine-tune the neutron flux within generic fuelassembly 30, so as to achieve a more precise burn-up of the fuel withingeneric fuel assembly 30.

Referring again to FIGS. 4 and 6, control rods 180 are selectivelyoperable, such as by means of respective ones of a plurality of drivemotors 210 controlled by a controller (not shown). Each drive motor 210engages its respective control rod 180 when electrical power is suppliedto motor 210 and suitably disengages control rod 180 when electricalpower is not supplied to motor 210, such as during a loss of powerincident. Thus, if a loss of power incident occurs, motor 210 willdisengage control rod 180, so that control rod 180 will verticallyslidably drop into generic fuel assembly 30 along an interior of thepreviously mentioned guide tube due to force of gravity. In this manner,control rods 180 will controllably supply negative reactivity to genericfuel assembly 30. Thus, generic fuel assembly 30, by means of controlrods 180, provides a reactivity management capability in the event of aloss of power incident, without reactor operator control orintervention.

Referring to FIG. 7, generic fuel assembly 30 may further comprise aneutron multiplier or reflector, which may take the form of a pluralityof elongate neutron reflector rods 220 sealingly housed in a reflectorrod cladding 230. Reflector rods 220 cause elastic scattering ofneutrons and are thus intended to “reflect” neutrons. Due to suchelastic scattering of neutrons, reflector rods 220 are capable ofintroducing positive reactivity into fuel assembly 30 by decreasing theneutron leakage from generic fuel assembly 30. In this regard, eachreflector rod 220 comprises a suitable neutron reflector material 240having a suitable probability for neutron scattering. In this regard,reflector material 240 may be a material selected from the groupconsisting essentially of beryllium (Be), lead alloys, tungsten (W),vanadium (V), depleted uranium (U), thorium (Th) and mixtures thereof.Reflector material 240 may also be selected from a wide variety of steelalloys. It should be appreciated that the fissile and fertile materialsthat are contemplated for use in generic fuel assembly 30 also have highelastic scattering cross sections.

Returning to FIG. 4, generic fuel assembly 30 further comprises acomparatively small and removable nuclear fission igniter 245 thatincludes moderate isotopic enrichment of nuclear fissionable material,such as, without limitation, U²³³, U²³⁵ or Pu²³⁹, suitably centered inenclosure 155 along a vertical axis 247 a. Igniter 245 may be disposedat an end of enclosure 155 rather than being centered in enclosure 155,if desired. Neutrons are released by igniter 245. The neutrons that arereleased by igniter 245 are captured by the fissile and/or fertilematerial within fuel rods 150 to initiate the previously mentionedfission chain reaction. Igniter 245 may be removed once the chainreaction becomes self-sustaining, if desired.

It will be understood that the teachings herein describe a travelingwave nuclear fission reactor. The basic principles of such a travelingwave nuclear fission reactor is disclosed in more detail in co-pendingU.S. patent application Ser. No. 11/605,943 filed Nov. 28, 2006 in thenames of Roderick A. Hyde, et al. and titled “Automated Nuclear PowerReactor For Long-Term Operation”, which application is assigned to theassignee of the present application, the entire disclosure of which ishereby incorporated by reference.

Referring to FIGS. 4, 8 and 9, there is shown a specific exemplary firstembodiment nuclear fission reactor fuel assembly, generally referred toas 250. Exemplary first embodiment fuel assembly 250 comprises a firstloading pattern, generally referred to as 260, for developing andmodulating neutron flux level (i.e., neutron population) in firstembodiment fuel assembly 250. First loading pattern 260 is shown at apredetermined instant in time after neutron ignition by igniter 245(e.g., 7.5 years after ignition). The terminology “modulating” isdefined herein to mean modifying or changing neutron flux level as afunction of time, space and/or energy. Modulating neutron flux levelmanages reactivity in first embodiment fuel assembly 250. In thismanner, the material composition of a region of the reactor is changed.This results in a change of the level of the effective neutronmultiplication factor, k_(eff), which in turn results in a change influx (modulation). As previously briefly mentioned and as disclosed inmore detail presently, first loading pattern 260 generates adeflagration wave or “burnfront” 270 that builds excess reactivity intofirst embodiment fuel assembly 250. Excess reactivity is developed forseveral reasons, one reason being that more fuel is bred than is burned.First loading pattern 260 balances this excess reactivity sufficientlybehind burnfront 270 (i.e., the space between igniter 245 and burnfront270) while allowing breeding within and in the vicinity of the front ofburnfront 270.

Referring to FIG. 10, a first control function, generally referred to as275, corresponding to first loading pattern 260 is shown in graphicalform comprising amount of control rod insertion in first embodiment fuelassembly 250 as a function of distance from igniter 245. As seen in FIG.10, the y-axis is the percentage amount of control rod inserted (thevalue is 100% behind burnfront 270 and 0% in front of burnfront 270).The x-axis is the distance from igniter 245 shown in units of meters. Inthe exemplary embodiment illustrated in FIG. 10, the x-axis has a lengthof approximately four meters. However, this distance may be any suitabledistance, such as four meters. This particular example shows a “limit”case. For example, burnfront 270 moves a distance, “x”, and a controlrod is fully inserted. Burnfront 270 then moves another distance “Δx”and another control rod is inserted. The step-wise control functionshown is a “binary” case. In practice, the reactor operator may deviatefrom the step-wise function. For example, the control rod closest toburnfront 270 may be in half-way or 50%. First control function 275modulates neutron flux at a level responsive to changes observed by amonitoring system, as described hereinbelow. As may be appreciated,enhanced steady state deflagration wave burnfront 270 propagation isestablished by means of a step-wise function type distribution ofcontrol material sufficiently behind burnfront 270. As an example,should the rate of reaction fall below desired levels at the front ofburnfront 270, a control function response could be to remove orrelocate absorber at the rear of the burnfront 270 such that the fissionrate increases. A neutron flux level is obtained and the controlfunction is readjusted to again maintain the desired condition. Bymoving the step function absorber closer to the front of burnfront 270such that a burn region fission rate is reduced the power can also bereduced. In accident scenarios, it is conceivable to deviate from thestep function configurations by placing sufficient absorber throughoutthe burn wave region.

Referring again to FIGS. 8, 9 and 10, first loading pattern 260comprises control rods 192/194 arranged behind burnfront 270 andcentered about a horizontal axis 247 b, as shown. First loading pattern260 further comprises fuel rods arranged into two groups. A first groupof fuel rods 280 includes fissile material (referred to herein as a“burning region”) and is arranged in a predetermined first group fuelrod pattern behind burnfront 270 and centered about axis 247 b, asdescribed hereinbelow. The burning region is primarily fertile materialwith some percentage of fissile material bred into it. A second group offuel rods 290 includes fertile fuel material and is arranged in apredetermined second group fuel rod pattern in front of burnfront 270and centered about axis 247 b, as shown. The terminology “in front ofburnfront 270” is defined to mean the space between propagatingburnfront 270 and an end of enclosure 155. The terminology “behindburnfront 270” is defined to mean the space between igniter 245 andburnfront 270.

Still referring to FIGS. 8, 9 and 10, when igniter 245 releases itsneutrons to cause “ignition”, and by way of example only and not by wayof limitation, two burnfronts 270 travel radially outwardly from igniter245 toward ends of enclosure 155, so as to form an oppositelypropagating wave-pair. As this occurs, burnfront 270 builds excessreactivity into first embodiment fuel assembly 250 as burnfront 270propagates from igniter 245 and into first group of fuel rods 280, whichare essentially depleted of fissile fuel material. This tends to leavesome excess reactivity behind burnfront 270. This result is undesirablebecause excess reactivity causes increased neutron fluence seen by fuelassembly structural materials in a region behind burnfront 270 wheresignificant burnup has already occurred.

Referring again to FIGS. 8, 9 and 10, it should be understood thatneutron flux generated by first group of fuel rods 280 behind burnfront270 breeds fissile fuel material in second group of fuel rods 290 infront of burnfront 270 by transmuting the fertile fuel material insecond group of fuel rods 290 into fissile fuel material at theburnfront's leading-edge. Transmuting the fertile fuel material insecond group of fuel rods 290 into fissile fuel material at theburnfront's leading-edge advances burnfront 270 in the direction ofarrows 295. As burnfront 270 sweeps over a given mass of fuel, fissileisotopes are continually generated as long as neutrons are present toundergo radiative capture in fertile nuclei. The rate at which fissileisotopes are generated may, for a given time and location within thereactor, exceed that of consumption of the fissile isotopes due toparasitic capture and fission. Additionally, capture of neutrons infertile material leads to intermediate isotopes which decay with a givenhalf-life to fissile material. Because the wave has a propagationvelocity, some amount of decay of intermediate isotopes, therefore,occurs behind burnfront 270. A combination of these effects results inadditional reactivity remaining and being generated behind burnfront270.

Thus, as shown in FIGS. 8, 9 and 10, burnfront 270 can be modulated toenable a variable nuclear fission fuel burnup. In this type of controlconfiguration, the propagation rate is enhanced by maintaining absorbersas far behind burnfront 270 as allowable to maintain power at a constantlevel. Biasing of the absorber material behind burnfront 270 counteractsthe build-up of excess reactivity within burnfront 270 without reducingthe amount of neutrons available for breeding in and in front ofburnfront 270. Thus, in order to propagate burnfront 270 in firstembodiment fuel assembly 250, burnfront 270 is initiated by igniter 245,as described above and then allowed to propagate. In one embodiment, theactively controllable control rods 192/194 insert neutron absorbers,such as without limitation, Li6, B10, or Gd, into first group of fuelrods 280 behind burnfront 270. Such an insertion of neutron absorbersdrives down or lowers neutronic reactivity of first group of fuel rods280 that is presently being burned by burnfront 270 relative toneutronic reactivity of second group of fuel rods 290 ahead of burnfront270, giving the wave a propagation direction indicated by arrow 295.Controlling reactivity in this manner increases the propagation rate ofburnfront 270 and therefore provides a means to control burn-up above aminimum value needed for propagation and a greater value set by, inpart, structural limitations discussed above.

Referring to FIG. 11 there is shown an exemplary second embodimentnuclear fission reactor fuel assembly, generally referred to as 300.Exemplary second embodiment fuel assembly 300 comprises a second loadingpattern, generally referred to as 310, for modulating neutron flux levelin second embodiment fuel assembly 300. Second loading pattern 310 isshown at a predetermined instant in time after neutron ignition byigniter 245 (e.g., 7.5 years after ignition). Modulating neutron fluxlevel manages reactivity in second embodiment fuel assembly 300. Asdisclosed in more detail presently, second loading pattern 310 generatesdeflagration wave or “burnfront” 270 that builds excess reactivity intosecond embodiment fuel assembly 300. Second loading pattern 310 balancesthis excess reactivity sufficiently in front of burnfront 270 whilereducing neutron fluence seen by fuel assembly. Control rods 192/194insert neutron absorbers into second group of fuel rods 290 in front ofthe burnfront 270, thereby slowing down the propagation of burnfront270. In this case, fuel to the left of burnfront 270 is allowed toproduce power as the burnfront propagates. One can see that such acontrol method could lead to the ignition of the entire fuel assembly300.

Referring to FIG. 12, a second control function, generally referred toas 320, corresponding to second loading pattern 310 is shown ingraphical form comprising amount of control rod insertion in secondembodiment fuel assembly 300 as a function of distance from igniter 245.Second control function 320 modulates neutron flux at a level responsiveto changes observed by a monitoring system, as described hereinbelow.Hence, increased steady state deflagration wave burnfront 270propagation in this embodiment is established by means of a step-wisefunction type distribution, as shown and is in part dependant on therate of removal of control rods 192/194.

Referring to FIG. 13 there is shown an exemplary third embodimentnuclear fission reactor fuel assembly, generally referred to as 330.Exemplary third embodiment fuel assembly 330 comprises a third loadingpattern, generally referred to as 340, for modulating neutron flux levelin third embodiment fuel assembly 330. Third loading pattern 340 isshown at a predetermined instant in time after neutron ignition byigniter 245 (e.g., 7.5 years after ignition). Modulating neutron fluxlevel manages reactivity in third embodiment fuel assembly 330. Asdisclosed in more detail presently, third loading pattern 340 generatesdeflagration wave burnfront 270 that builds excess reactivity into thirdembodiment fuel assembly 330. Third loading pattern 340 balances thisexcess reactivity sufficiently near burnfront 270 (i.e., the spacewithin or adjacent to burnfront 270) via control rods 192/194 whichinsert neutron absorbers into first group of fuel rods 280 within or tothe side of burnfront 270. By allowing build-up and/or utilization ofexcess reactivity at or near the perimeter of the burnfront, theeffective size and velocity of burnfront 270 may be modified.

Referring to FIG. 14, a third control function, generally referred to as350, corresponding to third loading pattern 340 is shown in graphicalform comprising amount of control rod insertion in third embodiment fuelassembly 300 as a function of distance from igniter 245. Third controlfunction 350 modulates neutron flux at a level responsive to changesobserved by a monitoring system, as described hereinbelow. Steady statedeflagration wave burnfront 270 propagation is established by means of acontinuous function type distribution, as shown.

Referring to FIG. 15, there is shown an exemplary fourth embodimentnuclear fission reactor fuel assembly, generally referred to as 360.Exemplary fourth embodiment fuel assembly 360 comprises a fourth loadingpattern, generally referred to as 370, for modulating neutron flux levelin fourth embodiment fuel assembly 360. Fourth loading pattern 370 isshown at a predetermined instant in time after neutron ignition byigniter 245 (e.g., 7.5 years after ignition). Modulating neutron fluxlevel manages reactivity in fourth embodiment fuel assembly 360. Asdisclosed in more detail presently, fourth loading pattern 370 generatesdeflagration wave burnfront 270 that builds excess reactivity intofourth embodiment fuel assembly 360. Fourth loading pattern 370 balancesthis excess reactivity sufficiently behind and in front of burnfront 370through use of control rods 192/194. Loading pattern 370 thereby givesan additional means to control wave size, propagation characteristics,and therefore burn-up and fluence. Alternatively, burnfront 270 may bestimulated “out front” by control rods 192/194 having fissile materialtherein.

Referring to FIG. 16, a fourth control function, generally referred toas 380, corresponding to fourth loading pattern 370 is shown ingraphical form comprising amount of control rod insertion in fourthembodiment fuel assembly 360 as a function of distance from igniter 245.Fourth control function 380 modulates neutron flux at a level responsiveto changes observed by a monitoring system, as described hereinbelow.Steady state deflagration wave burnfront 270 propagation is establishedby means of a function type distribution, as shown.

Referring to FIG. 17, there is shown an exemplary fifth embodimentnuclear fission reactor fuel assembly, generally referred to as 390.Exemplary fifth embodiment fuel assembly 390 comprises a fifth loadingpattern, generally referred to as 400, for modulating neutron flux levelin fifth embodiment fuel assembly 390. Fifth loading pattern 400includes reflector rods 220 in addition to fuel rods 150 and controlrods 192/194. As can be seen, by way of a non-limiting example, there isa repeating pattern of a row of absorber with a row of reflector behindthe row of absorber. Alternatively, the row of reflector may be locatedin front of the row of absorber. The reflector returns a portion of theleakage neutrons back towards the absorbing row (and burnfront 270)resulting in a need for less absorber and more neutrons in theburn/breed region. Fifth loading pattern 400 is shown at a predeterminedinstant in time after neutron ignition by igniter 245 (e.g., 7.5 yearsafter ignition). Modulating neutron flux level manages reactivity infifth embodiment fuel assembly 390. As disclosed in more detailpresently, fifth loading pattern 400 generates deflagration waveburnfront 270 that builds excess reactivity into fifth embodiment fuelassembly 390. Fifth loading pattern 400 balances this excess reactivitysufficiently behind burnfront 370 while reducing neutron fluence seen byfuel assembly materials behind the burnfront as a result of relativelyhigh burnup. Control rods 192/194 and reflector rods 220 modulateneutron flux in the first group of fuel rods 280 behind burnfront 270,thereby changing the effective size and propagation characteristics ofthe burnfront 270.

Referring to FIG. 18, a fifth control function, generally referred to as410, corresponding to fifth loading pattern 400 is shown in graphicalform comprising amount of control rod insertion in fifth embodiment fuelassembly 390 as a function of distance from igniter 245. Fifth controlfunction 410 modulates neutron flux at a level responsive to changesobserved by a monitoring system, as described hereinbelow. Steady statedeflagration wave burnfront 270 propagation is established by means of astep function type distribution, as shown. As with the embodiment shownin FIGS. 10 and 11, and as described above, this type of distributionleads to an enhanced burnfront propagation rate allowing for a reducedburn-up to achieved.

Referring to FIG. 19, there is shown an exemplary sixth embodimentnuclear fission reactor fuel assembly, generally referred to as 420.Exemplary sixth embodiment fuel assembly 420 comprises a sixth loadingpattern, generally referred to as 430, for modulating neutron flux levelin sixth embodiment fuel assembly 420. Sixth loading pattern 430 isobtained at a predetermined instant in time after neutron ignition byigniter 245 (e.g., 7.5 years after ignition). Modulating neutron fluxlevel manages reactivity in sixth embodiment fuel assembly 420. Asdisclosed in more detail presently, sixth loading pattern 430 generatesdeflagration wave burnfront 270 that builds excess reactivity into sixthembodiment fuel assembly 420. Sixth loading pattern 430 balances thisexcess reactivity sufficiently behind burnfront 270 and in front ofburnfront 270 while reducing neutron fluence seen by fuel assemblymaterials as a result of relatively high burnup. Control rods 192/194insert neutron absorbers into first group of fuel rods 280 behind and infront of burnfront 270, thereby changing the effective size of theburnfront 270. It may be appreciated that there may be other materialspresent besides absorber material.

Referring to FIG. 20, a sixth control function, generally referred to as440, corresponding to sixth loading pattern 430 is shown in graphicalform comprising amount of control rod insertion in sixth embodiment fuelassembly 420 as a function of distance from igniter 245. Sixth controlfunction 440 modulates neutron flux at a level responsive to changesobserved by a monitoring system, as described hereinbelow. Increasedsteady state deflagration wave burnfront 270 propagation is establishedby means of a continuous function type distribution, as shown.

Referring to FIG. 21, there is shown an exemplary seventh embodimentnuclear fission reactor fuel assembly, generally referred to as 450.Exemplary seventh embodiment fuel assembly 450 comprises a seventhloading pattern, generally referred to as 460, for modulating neutronflux level in seventh embodiment fuel assembly 450. Seventh loadingpattern 460 is shown at a predetermined instant in time after neutronignition by igniter 245 (e.g., 7.5 years after ignition). It should benoted that fuel rods 290 may have already been burnt. Modulating neutronflux level manages reactivity in seventh embodiment fuel assembly 450.As disclosed in more detail presently, seventh loading pattern 460generates deflagration wave burnfront 270 that builds excess reactivityinto seventh embodiment fuel assembly 450. Seventh loading pattern 460balances this excess reactivity sufficiently behind burnfront 370 whilereducing neutron fluence seen by fuel assembly materials as a result ofrelatively high burnup. Placing the control step function appropriatelyin front of burnfront 270 while adjusting the control reaction at therear of burnfront 270 may be performed to reverse the direction ofburnfront 270 propagation resulting in wave propagation throughpreviously burned rods 290. Control rods 192/194 insert neutronabsorbers into first group of fuel rods 280 that are now arranged behindburnfront 270, thereby changing the effective size of the burnfront 270.

Referring to FIG. 22, a seventh control function, generally referred toas 470, corresponding to seventh loading pattern 460 is shown ingraphical form comprising amount of control rod insertion in seventhembodiment fuel assembly 450 as a function of distance from igniter 245.Seventh control function 470 modulates neutron flux at a levelresponsive to changes observed by a monitoring system, as describedhereinbelow. Increased steady state deflagration wave burnfront 270propagation is established by means of a step function typedistribution, as shown.

It may be understood from the teachings hereinabove, that burnfront 270can be directed as desired according to selected propagation parametersmonitored by a monitoring system. For example, propagation parameterscan include a propagation direction or orientation of burnfront 270, apropagation rate of burnfront 270, power demand parameters such heatgeneration density, cross-sectional dimensions of a burning regionthrough which burnfront 270 is to the propagate (such as an axial orlateral dimension of the burning region relative to an axis ofpropagation of the burnfront 270), or the like. As another example, thepropagation parameters may be selected so as to control the spatial ortemporal location, profile and distribution of the burnfront 270, inorder to avoid possible failed or malfunctioning control elements (e.g.,neutron modifying structures or thermostats), failed or malfunctioningfuel rods, or the like. Failed or malfunctioning fuel rods may be due toswelling or cladding hot spots caused by coolant channel flow blockage.As another example, any ruptured broken fuel rod may be detected bymeans of feedback provided by detecting tracer isotopes placed withinthe fuel rods during manufacturing. As a further example, thepropagation parameters may be selected based on monitoring or sensingactinides by means of a gas monitor or by sensing of gamma radiation bymeans of a gamma radiation detector or “Geiger Counter”. As anotherexample, the propagation parameters may be selected based on monitoringdata from “coupons” responsive to neutron flux. As yet another example,the propagation parameters may be selected based on measurements oflocal temperature via thermocouples and flux via neutron detectors.

Referring to FIG. 23, a graph illustrates a linear relationship betweendeflagration wave burnfront velocity and burnup percent versus degree ofwave control function. As determined through neutronic simulation,position “A” on the graph corresponds to a step function type of controlof burnfront 270 while position “B” on the graph corresponds todistributed type control rod arrangement of burnfront 270. Position “A”corresponds to a configuration similar to that illustrated in FIGS. 9and 10, while Position “B” corresponds to a configuration similar tothat shown in FIGS. 13 and 14. Position “C” on the graph corresponds toa control configuration where absorber is distributed between that of astep function as shown in FIGS. 9 and 10 and that of the continuousfunction shown in FIGS. 13 and 14; i.e., the absorber is distributedmore behind the burnfront than in the distributed case, but not as muchas in the step function case. FIG. 23 relates to neutronic resultsobtained using the MCNPX-CINDER computer software code. In this regard,FIG. 23 shows that if absorber is used, placing the absorber into thereactor as a step function behind the wave gives the fastest wavevelocity and the lowest burn-up. Deviation from this configuration(distribute absorber throughout the wave) slows the wave and finally, ifabsorber is put in front of the wave, the wave's velocity should cease.

Referring to FIG. 23A, there is shown a graph illustrating an exemplaryspatial distribution of neutron flux, generally referred to as 475. Inthis regard, the graph plots spatial distribution 475 as neutron fluxversus distance from igniter 245. Spatial distribution 475 isrepresentative of the burnfront according to an exemplary controlfunction.

Referring to FIG. 23B, there is shown a graph illustrating a spatialprofile or control function, generally referred to as 477. Controlfunction 477 corresponds to spatial distribution 475 shown in FIG. 23A.FIG. 23B plots percent of control rod insertion versus distance fromigniter 245.

Referring to FIG. 23C, there is shown a graph illustrating an exemplaryspatial distribution of neutron flux, generally referred to as 479. Inthis regard, the graph plots spatial distribution 479 as neutron fluxversus distance from igniter 245. Spatial distribution 479 isrepresentative of the burnfront according to an exemplary controlfunction.

Referring to FIG. 23D, there is shown a graph illustrating a spatialprofile or control function, generally referred to as 481. Controlfunction 481 corresponds to spatial distribution 479 shown in FIG. 23C.This graph plots percent of control rod insertion versus distance fromigniter 245.

Referring to FIG. 23E, there is shown a graph illustrating an exemplaryspatial distribution of neutron flux, generally referred to as 483. Inthis regard, the graph plots spatial distribution 483 as neutron fluxversus distance from igniter 245. Spatial distribution 483 isrepresentative of the burnfront.

Referring to FIG. 23F, there is shown a graph illustrating a spatialprofile or control function, generally referred to as 485, correspondingto spatial distribution 483 shown in FIG. 23E. Spatial profile 485 has asteepest portion 487. This graph plots percent of control rod insertionversus distance from igniter 245.

It may be appreciated from the disclosure hereinabove that a burnupvalue at or below a predetermined burnup value is achievable. In thisregard, an amount of neutron absorber, reflector and/or emitter can becontrolled at a plurality of locations relative to burnfront 270, suchthat a majority of the neutron absorption occurs at locations behindburnfront 270 in order to obtain a burnup value at or below apredetermined burnup value. For example, the neutron emitter can bemoved from a first location behind burnfront 270 to a second location infront of burnfront 270 to achieve a desired burnup value at or below apredetermined burnup value.

In addition, it may be appreciated from the disclosure hereinabove thatradiation damage to one or more structural materials can also becontrolled in response to controlling burnup in generic fuel assembly 30and exemplary embodiment fuel assemblies 250/300/330/360/390/420/450. Inthis regard, controlling such radiation damage would entail achieving adesired radiation damage value, such as DPA, at or below a predeterminedradiation damage value. Achieving a radiation damage value at or below apredetermined radiation damage value may comprise moving a neutronemitter from a first location behind burnfront 270 to a second locationbehind burnfront 270. Alternatively, the neutron emitter can be movedfrom a first location behind burnfront 270 to a second location in frontof burnfront 270 to control potential radiation damage. As anotheralternative, an amount of neutron absorber can be controlled by means ofcontrol rods 192/194 at a location behind burnfront 270 to controlpotential radiation damage. In this regard, a majority of the neutronabsorption due to the neutron absorber may occur at locations behindburnfront 270. In addition, achieving a desired radiation damage valueat or below a predetermined radiation damage value may be obtained bycontrolling an amount of a neutron reflector at a location behindburnfront 270. In this regard, a majority of the neutron reflection dueto the neutron reflector may occur at locations behind burnfront 270.

It may also be appreciated from the disclosure hereinabove that theneutron flux may be selectively modulated at a location relative toburnfront 270. In this regard, the neutron flux may be modulated at alocation behind burnfront 270. In this case, a majority of themodulation occurs at a plurality of locations behind burnfront 270. Inaddition, selectively modulating neutron flux emitted by burnfront 270can entail selectively absorbing a portion of the neutron flux emittedby burnfront 270. In other words, an amount of neutron absorber iscontrolled at a location relative to burnfront 270. More generally, anamount of a neutron interactive material (e.g., insertion of controlrods 192/194) can be controlled at the location relative to burnfront270. In one embodiment, controlling the amount of neutron interactivematerial at the location relative to burnfront 270 comprises controllingan amount of neutron emitter at the location relative to burnfront 270.The neutron emitter can be a fissile element, a fertile element and/oran element capable of undergoing beta decay to a fissile element. On theother hand, controlling the amount of the neutron interactive materialat a location relative to burnfront 270 may comprise controlling anamount of a neutron reflector at the location relative to burnfront 270.

In addition, it may be appreciated from the disclosure hereinabove thatselectively modulating the neutron flux may be governed by a spatialprofile. The spatial profile can be either symmetric or asymmetric withrespect to burnfront 270. The spatial profile can have a slope having asteepest portion, the steepest portion suitably occurring at a locationbehind burnfront 270.

It may be further appreciated from the disclosure hereinabove thatselectively modulating neutron flux emitted by burnfront 270 maycomprise detecting a burning parameter associated with burnfront 270 andselectively modulating the neutron flux at least partially in responseto detecting the burning parameter. Detecting the burning parameter maycomprise monitoring material radiation damage, such as DPA, at least onelocation proximate burnfront 270; monitoring burnup at least onelocation proximate burnfront 270; monitoring burnup speed; monitoringburnfront breadth; monitoring one or more characteristics associatedwith the neutron flux at least one location proximate burnfront 270;monitoring nuclear radiation at least one location proximate burnfront270; and/or monitoring temperature at least one location thermallyproximate burnfront 270. Moreover, selectively modulating the neutronflux at least partially in response to detecting the burning parametermay comprise selectively modulating the neutron flux at least partiallyin response to detecting the burning parameter and detecting the burningparameter at least partially in response to a feedback control processand/or at least partially in response to a computer-based algorithmhaving a plurality of parameters associated with the burning parameter.In this regard, one or more of the parameters of the computer-basedalgorithm may be modified in response to detecting the burningparameter.

Illustrative Methods

Illustrative methods associated with exemplary embodiments forcontrolling burnup in a traveling wave nuclear fission reactor and fuelassembly will now be described.

Referring to FIGS. 24-65, illustrative methods are provided forcontrolling burnup in a traveling wave nuclear fission reactor and fuelassembly capable of emitting a neutron flux.

Turning now to FIG. 24, an illustrative method 490 for controllingburnup in a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 500. At a block 510, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor. The method 490 stops at a block 520.

Referring to FIG. 25, an illustrative method 530 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 540. At a block 550, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. The method 530stops at a block 560.

Referring to FIG. 26, an illustrative method 570 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 580. At a block 590, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 600,a predetermined burnup value is achieved. The method 570 stops at ablock 610.

Referring to FIG. 27, an illustrative method 620 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 630. At a block 640, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 650,a desired burnup value at or below a predetermined burnup value isachieved. The method 620 stops at a block 660.

Referring to FIG. 28, an illustrative method 670 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 680. At a block 690, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 700,the method comprises achieving a burnup value at or below apredetermined burnup value. At a block 710, an amount of a neutronabsorber is controlled at a location behind the burnfront. The method670 stops at a block 720.

Referring to FIG. 29, an illustrative method 790 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 800. At a block 810, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 820,a burnup value is achieved at or below a predetermined burnup value. Ata block 830, an amount of a neutron absorber achieving neutronabsorption is controlled at a plurality of locations relative to theburnfront and wherein a majority of the neutron absorption due to theneutron absorber is at a plurality of locations behind the burnfront.The method stops at a block 840.

Referring to FIG. 30, an illustrative method 850 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 860. At a block 870, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 880,a burnup value is achieved at or below a predetermined burnup value. Ata block 890, an amount of a neutron reflector is controlled at alocation behind the burnfront. The method stops at a block 900.

Referring to FIG. 31, an illustrative method 910 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 920. At a block 930, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 940,a burnup value is achieved at or below a predetermined burnup value. Ata block 950, an amount of a neutron reflector achieving neutronreflection is controlled at one or more locations relative to theburnfront and wherein a majority of the neutron reflection due to theneutron reflector is at a plurality of locations behind the burnfront.The method stops at a block 960.

Referring to FIG. 32, an illustrative method 970 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 980. At a block 990, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. At a block 1000,a burnup value is achieved at or below a predetermined burnup value. Ata block 1010, a neutron emitter is moved from a first location behindthe burnfront to a second location behind the burnfront. The methodstops at a block 1020.

Referring to FIG. 33, an illustrative method 1030 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1040. At a block 1050, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1060, a burnup value is achieved at or below a predeterminedburnup value. At a block 1070, a neutron emitter is moved from a firstlocation behind the burnfront to a second location proximate to theburnfront. The method stops at a block 1080.

Referring to FIG. 34, an illustrative method 1090 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1100. At a block 1110, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1120, a burnup value is achieved at or below a predeterminedburnup value. At a block 1130, a neutron emitter is moved from a firstlocation behind the burnfront to a second location in front of theburnfront. The method stops at a block 1140.

Referring to FIG. 35, an illustrative method 1150 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1160. At a block 1170, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1180, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. The method stops at a block 1190.

Referring to FIG. 36, an illustrative method 1200 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1210. At a block 1220, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1230, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1240, a radiation damage valueis achieved. The method stops at a block 1250.

Referring to FIG. 37, an illustrative method 1260 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1270. At a block 1280, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1290, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1300, a radiation damage valueis achieved at or below a predetermined radiation damage value. Themethod stops at a block 1310.

Referring to FIG. 38, an illustrative method 1320 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1330. At a block 1340, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1350, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1360, a radiation damage valueis achieved at or below a predetermined radiation damage value. At ablock 1370 a neutron emitter is moved from a first location behind theburnfront to a second location behind the burnfront. The method stops ata block 1380.

Referring to FIG. 39, an illustrative method 1390 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1400. At a block 1410, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1420, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1430, a radiation damage valueis achieved at or below a predetermined radiation damage value. At ablock 1440 a neutron emitter is moved from a first location behind theburnfront to a second location proximate to the burnfront. The methodstops at a block 1450.

Referring to FIG. 40, an illustrative method 1460 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1470. At a block 1480, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1490, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1500, a radiation damage valueis achieved at or below a predetermined radiation damage value. At ablock 1510, a neutron emitter is moved from a first location behind theburnfront to a second location in front of the burnfront. The methodstops at a block 1520.

Referring to FIG. 41, an illustrative method 1530 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1540. At a block 1550, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1560, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. At a block 1570, a radiation damage valueis achieved at or below a predetermined radiation damage value. Anamount of a neutron absorber is controlled at a location behind theburnfront at a block 1580. The method stops at a block 1590.

Referring to FIG. 42, an illustrative method 1600 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1610. At a block 1620, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1630, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. A radiation damage value is achieved at orbelow a predetermined radiation value at a block 1640. At a block 1650,an amount of a neutron absorber is controlled at a plurality oflocations relative to the burnfront and wherein a majority of theneutron absorption due to the neutron absorber is at a plurality oflocations behind the burnfront. The method stops at a block 1660.

Referring to FIG. 43, an illustrative method 1670 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1680. At a block 1690, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1700, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. A radiation damage value is achieved at orbelow a predetermined radiation value at a block 1710. An amount of aneutron reflector is controlled at a location behind the burnfront at ablock 1720. The method stops at a block 1730.

Referring to FIG. 44, an illustrative method 1740 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1750. At a block 1760, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. At ablock 1770, radiation damage to one or more structural materials iscontrolled in response to controlling a burnup value in the travelingwave nuclear fission reactor. A radiation damage value is achieved at orbelow a predetermined radiation value at a block 1780. At a block 1790,an amount of a neutron reflector achieving neutron reflection iscontrolled at a plurality of locations relative to the burnfront andwherein a majority of the neutron reflection due to the neutronreflector is at a plurality of locations behind the burnfront. Themethod stops at a block 1800.

Referring to FIG. 45, an illustrative method 1810 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1820. At a block 1830, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 1840. The method stops at a block 1850.

Referring to FIG. 46, an illustrative method 1860 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1870. At a block 1880, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 1890. At a block 1900, the neutron flux isselectively modulated at a location behind the burnfront. The methodstops at a block 1910.

Referring to FIG. 47, an illustrative method 1920 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1930. At a block 1940, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 1950. At a block 1960, the neutron flux isselectively modulated at a plurality of locations relative to theburnfront and wherein an amount of modulation at the plurality oflocations relative to the burnfront is governed by a spatial profile.The method stops at a block 1970.

Referring to FIG. 48, an illustrative method 1980 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 1990. At a block 2000, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2010. At a block 2020, the neutron flux isselectively modulated at a plurality of locations relative to theburnfront, so that a majority of the modulation of neutron flux occursat a plurality of locations behind the burnfront. The method stops at ablock 2030.

Referring to FIG. 49, an illustrative method 2040 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2050. At a block 2060, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2070. At a block 2080, a portion of the neutronflux is selectively absorbed at a location relative to the burnfront.The method stops at a block 2090.

Referring to FIG. 50, an illustrative method 2100 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2110. At a block 2120, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2130. At a block 2140, an amount of a neutronabsorber at the location relative to the burnfront is controlled. Themethod stops at a block 2150.

Referring to FIG. 51, an illustrative method 2160 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2170. At a block 2180, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2190. At a block 2200, an amount of a neutroninteractive material is controlled at the location relative to theburnfront. The method stops at a block 2210.

Referring to FIG. 52, an illustrative method 2220 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2230. At a block 2240, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2250. At a block 2260, an amount of a neutroninteractive material is controlled at the location relative to theburnfront. At a block 2270, an amount of a neutron emitter is controlledat the location relative to the burnfront. The method stops at a block2280.

Referring to FIG. 53, an illustrative method 2290 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2300. At a block 2310, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2320. At a block 2330, an amount of a neutroninteractive material is controlled at the location relative to theburnfront. At a block 2340, an amount of a neutron reflector iscontrolled at the location relative to the burnfront. The method stopsat a block 2350.

Referring to FIG. 54, an illustrative method 2360 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at block 2370. At a block 2380, the method comprisesmodulating the neutron flux emitted by the traveling wave nuclearfission reactor, the neutron flux defining a burnfront. The neutron fluxis selectively modulated at a location relative to the burnfront at ablock 2390. At a block 2400, a burning parameter associated with theburnfront is detected. At a block 2410, the neutron flux is selectivelymodulated at least partially in response to detecting the burningparameter associated with the burnfront. The method stops at a block2420.

Referring to FIG. 55, an illustrative method 2430 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2440. At a block 2450, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2460. At a block 2470, a burning parameterassociated with the burnfront is detected. At a block 2480, radiationdamage to a material at least one location proximate to the burnfront ismonitored. At a block 2490, the neutron flux is selectively modulated atleast partially in response to detecting the burning parameterassociated with the burnfront. The method stops at a block 2500.

Referring to FIG. 56, an illustrative method 2510 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2520. At a block 2530, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2540. At a block 2550, a burning parameterassociated with the burnfront is detected. At a block 2560, a burnupvalue is monitored at least one location proximate to the burnfront. Ata block 2570, the neutron flux is selectively modulated at leastpartially in response to detecting the burning parameter associated withthe burnfront. The method stops at a block 2580.

Referring to FIG. 57, an illustrative method 2590 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2600. At a block 2610, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2620. At a block 2630, a burning parameterassociated with the burnfront is detected. At a block 2640, burnupvelocity is monitored. At a block 2650, the neutron flux is selectivelymodulated at least partially in response to detecting the burningparameter associated with the burnfront. The method stops at a block2660.

Referring to FIG. 58, an illustrative method 2670 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2680. At a block 2690, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2700. At a block 2710, a burning parameterassociated with the burnfront is detected. At a block 2720, burnfrontbreadth is monitored. At a block 2730, the neutron flux is selectivelymodulated at least partially in response to detecting the burningparameter associated with the burnfront. The method stops at a block2740.

Referring to FIG. 59, an illustrative method 2750 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2760. At a block 2770, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2780. At a block 2790, a burning parameterassociated with the burnfront is detected. At a block 2800, one or morecharacteristics associated with the neutron flux are monitored at leastone location proximate to the burnfront. At a block 2810, the neutronflux is selectively modulated at least partially in response todetecting the burning parameter associated with the burnfront. Themethod stops at a block 2820.

Referring to FIG. 60, an illustrative method 2830 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 2840. At a block 2850, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 2860. At a block 2870, a burning parameterassociated with the burnfront is detected. At a block 2880, nuclearradiation is monitored at least one location proximate to the burnfront.At a block 2890, the neutron flux is selectively modulated at leastpartially in response to detecting the burning parameter associated withthe burnfront. The method stops at a block 2900.

Referring to FIG. 61, an illustrative method 3000 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 3010. At a block 3020, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 3030. At a block 3040, a burning parameterassociated with the burnfront is detected. At a block 3050, temperatureis monitored at least one location proximate to the burnfront. At ablock 3060, the neutron flux is selectively modulated at least partiallyin response to detecting the burning parameter associated with theburnfront. The method stops at a block 3070.

Referring to FIG. 62, an illustrative method 3080 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 3090. At a block 3100, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 3110. At a block 3120, a burning parameterassociated with the burnfront is detected. At a block 3130, neutron fluxis selectively modulated at least partially in response to detecting theburning parameter associated with the burnfront. At a block 3140, theneutron flux is selectively modulated at least partially in response todetecting the burning parameter in response to a feedback controlprocess. The method stops at a block 3150.

Referring to FIG. 63, an illustrative method 3160 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 3170. At a block 3180, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 3190. At a block 3200, a burning parameterassociated with the burnfront is detected. At a block 3210, the neutronflux is selectively modulated at least partially in response todetecting the burning parameter associated with the burnfront. At ablock 3220, the neutron flux is selectively modulated at least partiallyin response to detecting the burning parameter in response to acomputer-based algorithm. The method stops at a block 3230.

Referring to FIG. 64, an illustrative method 3240 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 3250. At a block 3260, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 3270. At a block 3280, a burning parameterassociated with the burnfront is detected. At a block 3290, the neutronflux is selectively modulated at least partially in response todetecting the burning parameter associated with the burnfront. At ablock 3300, the neutron flux is selectively modulated at least partiallyin response to detecting the burning parameter in response to acomputer-based algorithm, wherein the computer-based algorithmincorporates a plurality of parameters. At a block 3310, one or more ofthe plurality of parameters of the computer-based algorithm is modifiedin response to detecting the burning parameter. The method stops at ablock 3320.

Referring to FIG. 65, an illustrative method 3330 for controlling burnupin a traveling wave nuclear fission reactor capable of emitting aneutron flux starts at a block 3340. At a block 3350, the methodcomprises modulating the neutron flux emitted by the traveling wavenuclear fission reactor, the neutron flux defining a burnfront. Theneutron flux is selectively modulated at a location relative to theburnfront at a block 3360. At a block 3370, a burning parameterassociated with the burnfront is detected. At a block 3380, radiationdamage to one or more of a plurality of structural materials iscontrolled in response to selectively modulating the neutron flux. Themethod stops at a block 3390.

One skilled in the art will recognize that the herein describedcomponents (e.g., operations), devices, objects, and the discussionaccompanying them are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated.Consequently, as used herein, the specific exemplars set forth and theaccompanying discussion are intended to be representative of their moregeneral classes. In general, use of any specific exemplar is intended tobe representative of its class, and the non-inclusion of specificcomponents (e.g., operations), devices, and objects should not be takenas limiting.

Moreover, those skilled in the art will appreciate that the foregoingspecific exemplary processes and/or devices and/or technologies arerepresentative of more general processes and/or devices and/ortechnologies taught elsewhere herein, such as in the claims filedherewith and/or elsewhere in the present application.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true spirit and scope of the subject matter described herein.It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to claims containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that typically a disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms unless context dictates otherwise. For example, the phrase “Aor B” will be typically understood to include the possibilities of “A”or “B” or “A and B.”

With respect to the appended claims, those skilled in the art willappreciate that recited operations therein may generally be performed inany order. Also, although various operational flows are presented in asequence(s), it should be understood that the various operations may beperformed in other orders than those which are illustrated, or may beperformed concurrently. Examples of such alternate orderings may includeoverlapping, interleaved, interrupted, reordered, incremental,preparatory, supplemental, simultaneous, reverse, or other variantorderings, unless context dictates otherwise. Furthermore, terms like“responsive to,” “related to,” or other past-tense adjectives aregenerally not intended to exclude such variants, unless context dictatesotherwise.

Therefore, what are provided are a traveling wave nuclear fissionreactor, fuel assembly, and a method of controlling burnup therein.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.For example, each of the embodiments of the nuclear fission reactor fuelassembly may be disposed in a thermal neutron reactor, a fast neutronreactor, a neutron breeder reactor, a fast neutron breeder reactor, aswell as the previously mentioned traveling wave reactor. Thus, each ofthe embodiments of the fuel assembly is versatile enough to bebeneficially used in various nuclear reactor designs.

Moreover, the various aspects and embodiments disclosed herein are forpurposes of illustration and are not intended to be limiting, with thetrue scope and spirit being indicated by the following claims.

1. A method of controlling burnup in a traveling wave nuclear fissionreactor capable of emitting a neutron flux, comprising modulating theneutron flux emitted by the traveling wave nuclear fission reactor.
 2. Amethod of controlling burnup in a traveling wave nuclear fission reactorcapable of emitting a neutron flux, comprising modulating the neutronflux emitted by the traveling wave nuclear fission reactor, the neutronflux defining a burnfront.
 3. The method of claim 2, further comprisingachieving a predetermined burnup value.
 4. The method of claim 2,further comprising achieving a burnup value at or below a predeterminedburnup value.
 5. The method of claim 4, wherein achieving a burnup valueat or below the predetermined burnup value comprises controlling anamount of a neutron absorber at a location behind the burnfront.
 6. Themethod of claim 4, wherein achieving a burnup value at or below thepredetermined burnup value comprises controlling an amount of a neutronabsorber achieving neutron absorption at a plurality of locationsrelative to the burnfront and wherein a majority of the neutronabsorption due to the neutron absorber is at a plurality of locationsbehind the burnfront.
 7. The method of claim 4, wherein achieving aburnup value at or below the predetermined burnup value comprisescontrolling an amount of a neutron reflector at a location behind theburnfront.
 8. The method of claim 7, wherein the neutron reflectorcomprises a material chosen from beryllium (Be), lead (Pb), tungsten(W), vanadium (V), fertile material, steel alloys and mixtures thereof.9. The method of claim 4, wherein achieving a burnup value at or belowthe predetermined burnup value comprises controlling an amount of aneutron reflector achieving neutron reflection at one or more locationsrelative to the burnfront and wherein a majority of the neutronreflection due to the neutron reflector is at a plurality of locationsbehind the burnfront.
 10. The method of claim 4, wherein achieving aburnup value at or below the predetermined burnup value comprises movinga neutron emitter from a first location behind the burnfront to a secondlocation behind the burnfront.
 11. The method of claim 4, whereinachieving a burnup value at or below the predetermined burnup valuecomprises moving a neutron emitter from a first location behind theburnfront to a second location proximate to the burnfront.
 12. Themethod of claim 4, wherein achieving a burnup value at or below thepredetermined burnup value comprises moving a neutron emitter from afirst location behind the burnfront to a second location in front of theburnfront.
 13. The method of claim 2, further comprising controllingradiation damage to one or more structural materials in response tocontrolling a burnup value in the traveling wave nuclear fissionreactor.
 14. The method of claim 13, wherein controlling radiationdamage comprises achieving a radiation damage value.
 15. The method ofclaim 13, wherein controlling radiation damage comprises achieving aradiation damage value at or below a predetermined radiation damagevalue.
 16. The method of claim 15, wherein achieving the radiationdamage value at or below a predetermined radiation damage valuecomprises moving a neutron emitter from a first location behind theburnfront to a second location behind the burnfront.
 17. The method ofclaim 15, wherein achieving a radiation damage value at or below apredetermined radiation damage value comprises moving a neutron emitterfrom a first location behind the burnfront to a second locationproximate to the burnfront.
 18. The method of claim 15, whereinachieving a radiation damage value at or below a predetermined radiationdamage value comprises moving a neutron emitter from a first locationbehind the burnfront to a second location in front of the burnfront. 19.The method of claim 15, wherein achieving a radiation damage value at orbelow a predetermined radiation damage value comprises controlling anamount of a neutron absorber at a location behind the burnfront.
 20. Themethod of claim 15, wherein achieving a radiation damage value at orbelow a predetermined radiation damage value comprises controlling anamount of a neutron absorber achieving neutron absorption at a pluralityof locations relative to the burnfront and wherein a majority of theneutron absorption due to the neutron absorber is at a plurality oflocations behind the burnfront.
 21. The method of claim 15, whereinachieving a radiation damage value at or below a predetermined radiationdamage value comprises controlling an amount of a neutron reflector at alocation behind the burnfront.
 22. The method of claim 15, whereinachieving a radiation damage value at or below a predetermined radiationdamage value comprises controlling an amount of a neutron reflectorachieving neutron reflection at a plurality of locations relative to theburnfront and wherein a majority of the neutron reflection due to theneutron reflector is at a plurality of locations behind the burnfront.23. A method of controlling burnup in a traveling wave nuclear fissionreactor capable of emitting a neutron flux, comprising modulating theneutron flux emitted by the traveling wave nuclear fission reactor, theneutron flux defining a burnfront, wherein modulating the neutron fluxemitted by the traveling wave nuclear fission reactor comprisesselectively modulating the neutron flux at a location relative to theburnfront.
 24. The method of claim 23, wherein selectively modulatingthe neutron flux at a location relative to the burnfront comprisesselectively modulating the neutron flux at a location behind theburnfront.
 25. The method of claim 23, wherein selectively modulatingthe neutron flux at a location relative to the burnfront comprisesselectively modulating the neutron flux at a plurality of locationsrelative to the burnfront and wherein an amount of modulation at theplurality of locations relative to the burnfront is governed by aspatial profile.
 26. The method of claim 25, wherein the spatial profileis symmetric with respect to the burnfront.
 27. The method of claim 25,wherein the spatial profile is asymmetric with respect to the burnfront.28. The method of claim 25, wherein the spatial profile has a slopehaving a steepest portion and wherein the steepest portion of the slopeof the spatial profile occurs at a location behind the burnfront. 29.The method of claim 23, wherein selectively modulating the neutron fluxat a location relative to the burnfront comprises selectively modulatingthe neutron flux at the location relative to the burnfront, so that amajority of the modulation of neutron flux occurs at a plurality oflocations behind the burnfront.
 30. The method of claim 23, whereinselectively modulating the neutron flux at a location relative to theburnfront comprises selectively absorbing a portion of the neutron fluxat the location relative to the burnfront.
 31. The method of claim 23,wherein selectively modulating the neutron flux at a location relativeto the burnfront comprises controlling an amount of a neutron absorberat the location relative to the burnfront.
 32. The method of claim 31,wherein the neutron absorber comprises a material chosen from lithium,silver, indium, cadmium, boron, cobalt, hafnium, dysprosium, gadolinium,samarium, erbium, europium and mixtures thereof.
 33. The method of claim31, wherein the neutron absorber comprises a compound chosen fromsilver-indium-cadmium alloy, boron carbide, zirconium diboride, titaniumdiboride, hafnium diboride, gadolinium titanate, dysprosium titanate andmixtures thereof.
 34. The method of claim 23, wherein selectivelymodulating the neutron flux at a location relative to the burnfrontcomprises controlling an amount of a neutron interactive material at thelocation relative to the burnfront.
 35. The method of claim 34, whereincontrolling the amount of the neutron interactive material at thelocation relative to the burnfront comprises controlling an amount of aneutron emitter at the location relative to the burnfront.
 36. Themethod of claim 35, wherein the neutron emitter comprises a fissileisotope.
 37. The method of claim 35, wherein the neutron emittercomprises a fertile isotope.
 38. The method of claim 35, wherein theneutron emitter comprises an element capable of undergoing beta decay tobecome a fissile isotope.
 39. The method of claim 34, whereincontrolling the amount of the neutron interactive material at thelocation relative to the burnfront comprises controlling an amount of aneutron reflector at the location relative to the burnfront.
 40. Themethod of claim 23, further comprising: detecting a burning parameterassociated with the burnfront; and selectively modulating the neutronflux at least partially in response to detecting the burning parameterassociated with the burnfront.
 41. The method of claim 40, whereindetecting a burning parameter associated with the burnfront comprisesmonitoring radiation damage to a material at least one locationproximate to the burnfront.
 42. The method of claim 40, whereindetecting a burning parameter associated with the burnfront comprisesmonitoring a burnup value at least one location proximate to theburnfront.
 43. The method of claim 40, wherein detecting a burningparameter associated with the burnfront comprises monitoring burnfrontvelocity.
 44. The method of claim 40, wherein detecting a burningparameter associated with the burnfront comprises monitoring burnfrontbreadth.
 45. The method of claim 40, wherein detecting a burningparameter associated with the burnfront comprises monitoring one or morecharacteristics associated with the neutron flux at least one locationproximate to the burnfront.
 46. The method of claim 40, whereindetecting a burning parameter associated with the burnfront comprisesmonitoring nuclear radiation at least one location proximate to theburnfront.
 47. The method of claim 40, wherein detecting a burningparameter associated with the burnfront comprises monitoring temperatureat least one location thermally proximate to the burnfront.
 48. Themethod of claim 40, wherein selectively modulating the neutron flux atleast partially in response to detecting the burning parameter comprisesselectively modulating the neutron flux at least partially in responseto detecting the burning parameter in response to a feedback controlprocess.
 49. The method of claim 40, wherein selectively modulating theneutron flux at least partially in response to detecting the burningparameter comprises selectively modulating the neutron flux at leastpartially in response to detecting the burning parameter at leastpartially in response to a computer-based algorithm.
 50. The method ofclaim 49, wherein the computer-based algorithm incorporates a pluralityof parameters.
 51. The method of claim 50, wherein selectivelymodulating the neutron flux at least partially in response to detectingthe burning parameter in response to the computer-based algorithmincorporating the plurality of parameters comprises modifying one ormore of the plurality of parameters of the computer-based algorithm inresponse to detecting the burning parameter.
 52. The method of claim 40,further comprising controlling radiation damage to one or more of aplurality of structural materials in response to selectively modulatingthe neutron flux. 53.-113. (canceled)